Device for recording switching impulses



March 27, 1962 Filed Aug. 25, 1959 H. THIELE ETAL DEVICE FOR RECORDINGSWITCHING IMPULSES 2 Sheets-Sheet 1 March 27, 1962 H. THIELE ETAL3,026,769

DEVICE FOR RECORDING SWITCHING IMPULSES Filed Aug. 25, 1959 2Sheets-Sheet 2 United States Patent Qfiice DEVICE FOR RECORDINGSWITCHING IMPULSES Heinz Thieie, Kiel-Wilt, and Arno Ritze, Kiel,Germany,

assignors to Zeiss Ilton Aktiengesellschait, Stuttgart,

Germany Filed Aug. 25, 1959, Ser. No. 836,016 Claims priority,application Germany Aug. 29, 1958 3 Claims. (Cl. 88-28) The inventionrelates to improvements in a device for recording switching-impulses onone of two separate sound tracks of a sound tape moving in the samedirection for the purpose of controlling a projector, while the othersound track is a carrier of a speech or other sounds, such as a musicalcomposition or the like.

The object of the invention is to perform the projection of slidesautomatically and in dependence of a sound rendition or a speechexplaining the pictures on the slides.

It has already been suggested previously to arrange on a magnetic soundband in addition to the recorded speech or other sounds, individualcontact strips in such a se quence that the slide change of theprojector may be performed as a function of the recording on the band.However, such contact strips on a magnetic sound band have not provedsuccessful. Therefore, another method has been adopted which uses twoseparate sound tracks running in the same direction, one of which servesas a carrier of speech and/or other sounds, while on the other soundtrack a control frequency is recorded which, after being scanned andamplified accordingly, operates the slide changer to cause the projectorto project the next slide onto the screen.

A well known method of this type operates with a fast decaying frequencyof 1000 p.p.s., which otters the advantage that for the recording ofthis control-frequency only an impulse-generator is required whichrequires only minor switching means. As against this advantage, thereis, however, the disadvantage that the decay-period of such a frequencyis constant, whereas the changing periods of projectors varyconsiderably with their construction. There is, however, the possibilityto employ an additional relay-circuit so as to adapt the constantcontrol-period to the varying changing periods of the projector. This,however, is to be regarded as an avoidable complication which can beaverted, according to the present invention, by providing the previouslymentioned device with special means, which make the recording period ofthe control impulses a function of the changing period of the projector.For practical purposes, a push button is employed, which operates theslide-changing device as well as connects the recording device to theoscillator or frequencygenerator which latter supplies the switchingimpulses. Since the push button remains in an operative position untilthe slide change is completed, the length of switching impulses isthereby fixed.

For generating electric waves a generator or oscillator is required, incontrast to the well known device mentioned above. This, however, doesnot result in a real complication if the amplifier device required forthe reproduction of the switching impulses is made use of as a feedbackoscillator for the modulation period. Preferably, a direct currentis impressed upon the switching impulses, required for recording, in awell known manner, for the purpose of obtaining an optimal operationpoint on the hysteresis curve. Such a direct current biasing issufficient, since the value of the non-linear harmonic distortion factorneed not be considered, contrary to conditions in the method ofrecording and reproduction of sound entertainment. It is desirable toperform the obliterating method with one and the same magnet-head andthis is achieved by the fact that the push button in its non-operatingposition closes a DC. circuit over the magnet-head, when set forrecording.

In accordance with the present invention the entire device for therecording and reproduction of switching impulses is constructed as aunit having its own main supply and amplifier. The device is connectedto the projector only by the switching line, and is connected with thesound apparatus only by the sound track.

The main advantage obtained with a device of this type is thepossibility to use it with any type of projector and any sound bandapparatus. There is no need for any act to change the construction ofthe sound band apparatus or of the projector.

The invention is illustrated in the drawings as follows:

FIG. 1 shows a block diagram, and

MG. 2 shows the circuit diagram of the control device.

One of the two sound tracks on the sound tape 2 is provided with arecord which after reproduction is erased within the sound device 1 inthe usual manner. In order to provide the other sound track withswitching impulses, the sound tape 2 is led over suitable guide rollerspast a magnet head 3 of the control device 4. The coil 5 of the magnethead 3 is arranged in series with the transistor stages 6 and '7 and therelay 8 which latter operates the contact 9 located in the controlcircuit 10 of the slide.

changer 22 of the projector 11. A preferred embodiment of the slidechanger 22 is disclosed in the German patent application Z 7154 IX/42h,filed February 25, 1959.

The circuit of magnet coil 5 also contains a push button switch 12. Thesound device 1, the control device 4 and the projector 11 have each aseparate connection to supply lines 13, 14 and 15 respectively.

The input transformer 16 (FIG. 2) of the control device 4 is connectedto a rectifier l7, supplying the required direct current to the controldevice. The two transistor stages 6 and 7 are arranged in the usualmanner and include in their circuit an autotransformer 24. To the outputside of the last transistor stage is connected the relay 8 with itscontrol contact 9 over the rectifier l8 and autotransformer 23. When themulti-switch 19 is in its left hand position as indicated by the leftend of the double arrow 25 in FIG. 2, namely to reception, and the pushbutton switch 12 is not operated, then a direct current energizes themagnet head 3 and thereby erases any recordings which may be present onthe respective sound track.

When the push button switch 12 is opened by a pressure of the operatorthis direct current supply is cut off. At the same time the output oftransistor stage 7 is connected to the magnet head 3 and relay 8 isconnected to the D.C. voltage. Through the first mentioned procedure afeed back voltage is supplied to magnet head 3. Condenser 20 and magnetcoil 5 form a resonance circuit tuned to about 1000 p.p.s. The notedfeed back voltage in conjunction with the condenser circuit generatesswitching impulses up to the moment the push button switch 12 isreleased by the operator. This release of the push button switch,however, occurs only after the slide change in the projector iscompleted. Therefore, the switching impulses are positively recorded ontheir sound track of such a length as required for the change of a slideby the projector. The selected arrangement of the control devicesupplies a direct current component to the feed-back voltage. The choiceof the size or value of this component determines the operating point onthe magnetic hysteresis curve.

When the multi-contact change-over switch 19 is in the right handposition of reproduction, as shown in the drawing, the magnet head 3 isconnected to the input circuit of the transistor. The output of thetransistor is connected over rectifier 18 with the relay so that theswitching impulses appearing on the sound track operate the PatentedMar. 27, we:

relay 8 with the required length of time and thereby cause by means ofthe control circuit 10 a slide change in the projector.

What we claim is:

1. In a device for recording switching impulses upon a magnetic soundtape provided with two separate sound tracks moving in the samedirection, of which one sound track carries a record of speech, music orthe like, while the other sound track is used for controlling theoperation of the slide changer of a slide projector, including amanually operable switch in circuit with a frequency generator fordetermining the length of the recording time of switching impulses onsaid other sound track in dependence of the time for starting the changeof the slides to be projected by the slide projector, another circuitincluding a transistor for energizing said frequency generator, amagnetic sound head adapted to be employed for the recording of saidswitching impulses and also as a reproducing and erasing head, and achange-over switch for connecting said magnetic sound head into itsrecord ing position with the output of said transistor and in itsreproducing position with the input of said transistor.

2. In a device for recording switching impulses upon a magnetic soundtape provided with two separate sound tracks moving in the samedirection, of which one sound track carries a record of speech, music orthe like, while the other sound track is used for controlling theoperation of the slide changer of a slide projector, including means fordetermining the length of the recording time of switching impulses onsaid other sound track in dependence of the time for starting the changeof the slides to be projected by the slide projector, said meansinc1uding a push button switch arranged in a circuit with a frequencygenerator, said push button switch when moved to open position effectinga connection of the recording device with said frequency generator aslong as the slide is 4 to be projected, said push button switch when inposition disconnecting said frequency generator and closing a directcurrent circuit which includes a magnetic sound head adapted forrecording said magnetic sound head when energized by direct currentoperating as erasing head.

3. In a device for recording switching impulses upon a magnetic soundtape provided with two separate sound tracks moving in the samedirection, of which one sound track carries a record of speech, music orthe like, while the other sound track is used for controlling theoperation of the slide changer of a slide projector, including means fordetermining the length of the recording time of switching impulses onsaid other sound track in dependence of the time for starting the changeof the slides to be projected by the slide projector, said switchingimpulse recording device including a normally closed switch which duringthe recording is manually held open during the period of time a slide isto be projected, said switching impulse recording device forming with atransistor a selfcontained unit provided with its own terminals to beconnected to a source of current supply, and a switching circuitcontrolled by said transistor forming the only connection of said unitwith said projector, while said magnetic sound tape forms the onlyconnection between said transistor and another device which provides thefirst mentioned sound track with a record of speech, music or the like.

References Cited in the file of this patent UNITED STATES PATENTS2,631,855 Kornei Mar. 17, 1953 2,787,669 Plan et a1 Apr. 2, 19572,811,588 Julie Oct. 29, 1957 2,847,513 Schlafiy Aug. 12, 1958 2,889,742Marturano June 9, 1959

